In popular culture and UFO conspiracy theories, men in black (MIB) are men dressed in black suits who claim to be government agents and who harass or threaten UFO witnesses to keep them quiet about what they have seen. It is sometimes implied that they may be aliens themselves. The term is also frequently used to describe mysterious men working for unknown organizations, as well as various branches of government allegedly designed to protect secrets or perform other strange activities. The term is generic, used for any unusual, threatening or strangely behaved individual whose appearance on the scene can be linked in some fashion with a UFO sighting.
Men in black figure prominently in ufology and UFO folklore. In 1947, Harold Dahl claimed to have been warned not to talk about his alleged UFO sighting on Maury Island by a man in a dark suit. In the mid 1950s, the ufologist Albert K. Bender claimed he was visited by men in dark suits who threatened and warned him not to continue investigating UFOs. Bender believed the men in black were secret government agents tasked with suppressing evidence of UFOs. The ufologist John Keel claimed to have had encounters with men in black and referred to them as "demonic supernaturals" with "dark skin and/or “exotic” facial features". According to the ufologist Jerome Clark, reports of men in black represent "experiences" that "don’t seem to have occurred in the world of consensus reality".
In his article, "Gray Barker: My Friend, the Myth-Maker," John C. Sherwood claims that, in the late 1960s, at the age of 18, he cooperated when Gray Barker urged him to develop a hoax – which Barker subsequently published – about what Barker called "blackmen", three mysterious UFO inhabitants who silenced Sherwood's pseudonymous identity, "Dr. Richard H. Pratt".
Blue Öyster Cult directly mention the Men In Black in the lyrics to two of their songs. In the opening verse of 1976's "E.T.I (Extra Terrestrial Intelligence)" we are told: I hear the music, daylight disc, Three men in black said, "Don't report this". Then in 1983's "Take me away": Don't ask if they are real, The men in black, their lips are sealed.
Alternative rock band C.E.IV wrote and recorded a song titled 'Mib Men' in 1985. It appeared in their 1988 concept album 'Abduction' during a sequence where an abductee was chased by men in black. The song was re-recorded for their 1993 compilation album 'Visions of C.E.IV'. 
In the role-playing game Mage: The Ascension, the Men In Black are an arm of the New World Order, a convention of technology-focused mages that use information control and espionage to enforce the scientific paradigm. 
The Steve Jackson Games volunteer demonstration program are called the "Men In Black" where the members of which are known as "MIBs." Members of this program attend local conventions and visit game stores to promote awareness of Steve Jackson Games products. 
Frank Black, the singer for The Pixies also known by the pseudonym Black Francis, released a single entitled "Men in Black" in 1995 which subsequently appeared on his album The Cult of Ray. He described the song in 1996 by stating that "it's about the Men in Black who are the psychological intimidators sent by the alien or maybe the government or maybe both."
In Season 3, Episode 20 of The X-Files, "Jose Chung's From Outer Space", a man in a black suit, hat and gloves appears to warn and threaten a character in the episode not to share his experience witnessing an alien abduction. Another man in black also shows up in the episode and is played by Alex Trebek. The first man in black is played by Jesse Ventura.
The British TV series Doctor Who features a race of aliens known as The Silence that appear to be dressed in black suits. These beings work behind the scenes altering the course of human history to their own ends, and cannot be remembered by those who see them. The only trace of their presence is either a vague memory or subconscious image of their appearance, or the hypnotic suggestions they leave during their encounters. The concept and appearance of The Silence partially draw upon the myth of the Men in Black.
The Mothman Prophecies - 1975 book by John Keel an account of alleged sightings of a large, winged creature called Mothman in the vicinity of Point Pleasant, West Virginia, during 1966 and 1967, it also narrates encounters of the author with “Men In Black”